Process for the preparation of diphenols

ABSTRACT

A PROCESS IS DISLCOSED FOR MAKING CATECHOL AND HYDROQUINONE USING HYDROGEN PEROXIDE TO HYDROXYLATE PHENOL IN THE PRESENCE OF A C1-4 ALKANOIC ACID USING TRIFLUOROACETIC ACID AS A CATALYST. THE REACTION TEMPERATURE IS FROM 50*-100* C. AND THE MOLAR RATIO OF PHENOL: HYDROGEN PEROXIDE IS FROM 4:1 TO 20:1.

United States Patent 3,836,591 PROCESS FOR THE PREPARATION OF DIPHENOLS Paolo Maggioni, Moutevecchio, Italy, assignor to Brichima S.p.A., Milan, Italy No Drawing. Filed Jan. 17, 1972, Ser. No. 218,557

Claims priority, application Italy, July 17, 1971, 26,963/71 Int. Cl. C07c 37/00 US. Cl. 260-'-621 G 1 Claim ABSTRACT OF THE DISCLOSURE A process is disclosed for making catechol and hydroquinone using hydrogen peroxide to hydroxylate phenol in the presence of a C alkanoic acid using trifiuoroacetic acid as a catalyst. The reaction temperature is from 50-100 C. and the molar ratio of phenol:hydrogen peroxide is from 4:1 to 20: 1.

The present invention is concerned with a new process for the preparation of diphenols. More precisely the present invention is concerned with an industrial process which gives high yields, of hydroquinone and catechol under economical convenient conditions, starting from phenol, with a prevalence of the ortho-isomer.

The industrial importance of diphenols is well known (see for example Kirk-Othmer Encyclopedia Chem. Technolog, second ed., vol. 11, page 462 (1966)) wherein many reactions and processes were studied for the preparation of diphenols.

However these processes are not quite satisfactory from the point of view of industrial realization and in particular, in so far as catechol is concerned, it is preferably prepared by extraction from natural products rather than by chemical synthesis.

Among the many considered reactions, the direct hydroxylation 'of phenol by means of hydrogen peroxide has been particularly studied (see for example Merz, J. K. andW. A. WatersJ. Chem. Soc. (1949): Loebl, Stein and Weiss, J. Chem. Soc. 2074 (1949); G. R. A. Johnson, G. Stein and Weissl. Chem. Soc. 3275 (1951); E. Boyland, P. Sims-J. Chem. Soc. 2967 (1953);.1. O. Konecnyl. Am. Soc. 76, 4993 (1954)). None, however, lead to an economically convenient process due to the low yields caused by the fact that diphenols are more sensible to the hydroxylating and oxydizing action of hydrogen peroxide than phenol; it is thus extremely difiicult to control the reaction in such a manner to have it terminated when the primary oxydated product is formed (G. Stein and I. Weiss, J. Chem. Soc. 3265 (1951); S. I. Cosgreve and W. A. Waters, 1. Chem. Soc. 1726 (1951).

Particularly speaking, hydroquinone and catechol are very easily oxydatedto the corresponding quinones and successively degraded, so that as soon as the concentration of diphenols in the reaction mixture reaches an appreciable level, their further degradation competes with the primary oxydation of phenol.

We have now surprisingly found that if the direct l1? droxylation of phenol with hydrogen peroxide is performed in the presence of particular acid catalysts and organic monocarboxylic acids having from 1 to 4 carbon atoms, under particular conditions of temperature and hydrogen peroxide concentration, it is possible to obtain a mixture of catechol and hydroquinone in very high yields and economically convenient conversions.

The reaction on which the present invention is based, may be schematically represented as follows:

3,836,591 Patented Sept. 17, 1974 Two factors are determinant in carrying out the process according to the present invention: the kind of acid catalysis and the hydrogen peroxide concentration in the reaction mixture. This will extenuate the further attack of diphenols resulting in high yields of catechol and hydroquinone based upon converted phenol.

The acid catalysts which constitute a characteristic feature of the process according to the present invention, are inorganic and organic acids, selected from the group consisting of trifluoroacetic acid, and acids having a pK comprised between 0.7 and 3, preferably mono-, di-, tri-chloro acetic acid, oxalic acid, phosphoric acid, benzene, and toluene-sulphonic acids.

The monocarboxylic organic acids which must be used together with the above indicated acid catalysts are, formic, acetic, propionic and butyric acid. Particularly convenient from an economical point of view is acetic acid.

The amount of catalyst to be used, with respect to the reacted phenol, lies between comparatively wide limits, depending on the acid selected for use. In any case, however, the amount of acid is preferably between 0.03 and 10% mol. with respect to phenol. It has been found for example that the preferred amount of trifiuoroacetic acid to be used is between 0.2 and 10%.

The weight ratio between the acid catalyst and the monocarboxylic organic acid is preferably between 1:5 and 1:50.

We have also found that in the group of acid catalysts to be used to realize the process of the present invention, trifiuoroacetic acid allows particularly mild temperature conditions and thus of realizing a process particularly convenient from an industrial point of view.

More precisely phenol reacts with hydrogen peroxide, in the presence of trifiuoroacetic acid and monocarboxylic C organic acids in the above defined proportion, at a temperature between 0 and 50 C. (in particular at room temperature), with a comparatively short reaction time.

The molar ratio of phenol:hydrogen peroxide is preferably between 20:1 and 4: 1.

We have also found that the remaining catalysts accord? ing to the present invention, having a pK between 0.7 and 3, in addition to needing slightly higher temperatures than trifluoroacetic acid, when accelerating the transformation reaction of phenol into catechol and hydroquinone with hydrogen peroxide, in a practically useful reaction time at temperatures between 50 and 100 C., also need a sufficient concentration of H 0 with respect to phenol in the reaction mixture in order to achieve high yields of diphenols based upon the converted phenol.

More precisely it is necessary to keep a minimum concentration of 5% of hydrogen peroxide with respect to phenol, and preferably a concentration ranging between 5 and 15%, by continuously feeding H 0 in the reaction mixture in order to restore the reacted amount. As a matter of fact we have found that with the indicated catalysts using concentrations of hydrogen peroxide lower than 5% but as dilutions increase (the remaining conditions being identical) the oxydizing action of hydrogen peroxide is remarkably increased and the hydroxylating action correspondingly decreased.

The catalysts according to the invention are preferably selected, from the group consisting of mono-, di-trichloro acetic acid, oxalic acid, phosphoric acid and, benzenand toluen-sulphonic acids. They are used in amounts between 0.03 and with respect to phenol.

In any case, in the process according to the present invention, it is preferred to maintain the conversion of phenol lower than 40%.

The yields in diphenols which may be reached are be tween 80 and 95%. Higher yields are also possible.

It is preferred, when the reaction is completed, to submit the reaction mixture to fractional distillation in order to recover the monocarboxylic acid, the catalyst and the excess of phenol which are directly recycled, it also allows one to separate catechol and hydroquinone in the pure state.

Only a slight residue of non volatile substances remain.

In order to better clarify the various features of the present invention and how to perform them, we give hereinafter some illustrative examples. These examples are not intended to limit the invention.

EXAMPLE 1 Into a 1 liter, 4 neck-flask, provided with stirrer, reflux cooler, thermometer and feeding funnel, 293 g. of phenol, 9.4 ml. of formic acid and 1.9 ml. of trifluoroacetic acid are introduced; then the mixture is heated to 40 C. and is added to a mixture consisting of 25 .7 ml. of formic acid and 24 ml. of 39% hydrogen peroxide over a period of 8 minutes.

After 4 hours 8.64 g. of hydrogen peroxide are consumed.

A sample of the reaction mixture is transformed into methyl ether and gas-chromatographically analyzed by using 4-methyl-veratrol and p.cresolmethylether as internal standards.

The reaction mixture when tested shows a content of 7.95 g. hydroquinone, 12.45 catechol and 271.2 g. of phenol. The overall yield in diphenols is 93.5%.

Distilling under vacuum the peroxy components, the carboxylic acid and the catalyst are recovered; then phenol (270 g.), catechol (12.3 g.) and hydroquinone are separated.

EXAMPLE 2 Into a 1 liter, 4 neck-flask, equipped with stirrer, thermometer, reflux cooler and feeding funnel, are poured 293 g. of phenol, 2.5 of 99% phosphoric acid and 14.2 ml. of glacial acetic acid. The reaction mixture is heated to 80 C. and added to a mixture consisting of 39 m1. of glacial acetic acid and 24 ml. of 39% hydrogen peroxide over a period of 8 minutes. The concentration of hydrogen peroxide is kept constant by continuously feeding new H 0 After 3 hours 10.58 g. of hydrogen peroxide are consumed.

A sample of the reaction mixture is gas-chromatographically analyzed with the method of the internal standard, after having been transformed into methyl others as in the preceding examples.

The reaction mixture contains 13.8 g. of catechol, 8.45 g. of hydroquinone and 267.3 g. of phenol. Yield on the phenol is equal to 86.5%. Distilling the reaction mixture under vacuum the peroxy reagents, the carboxylic acid and phenol (266.5 g.), catechol (13.7 g.) and hydroquinone (8.2 g.) are recovered.

4 EXAMPLE 3 Into a 1 liter, 4 neclbflask, equipped with stirrer, reflux cooler, feeding funnel and thermometer are poured, 293 g. of phenol, 2.5 g. of 99% phosphoric acid and 14.2 ml. of glacial acetic acid. The mixture is warmed to C. and added to a mixture consisting of 39 ml. of glacial acetic acid and 24 ml. of 39% hydrogen peroxide over a period of 8 minutes. After keeping the mixture for 6 hours at 80 C., 9.52 g. of hydrogen peroxide are consumed. A sample is analyzed as in Example 2. An overall content'of 7 g. catechol, 3.78 g. hydroquinone and 272.5 g. of phenol is found.

Diphenols yield as high as 52.5%. By distilling under vacuum, as in Example 2, 271.5 g. of phenol, 6.9 g. of catechol and 3.65 g. of hydroquinone are recovered.

EXAMPLE 4 Into a 1 liter, 4 neck-flask equipped with stirrer, thermometer, reflux cooler and feeding funnel, are poured 293 g. of phenol, 4 g. of trichloroacetic acid and 9.4 ml. of formic acid.

The reaction mixture is heated to 60 C. and added to a mixture consisting of 25.7 ml. of formic acid and 24 ml. of 39% hydrogen peroxide. The hydrogen peroxide concentration is kept constant by continuously feeding fresh hydrogen peroxide.

12 g. of hydrogen peroxide are consumed after 40 minutes. A sample is gas-chromatographically analyzed as in Example 2.

The mixture was found to consist of 15.62 g. of catechol, 9.98 g. of hydroquinone and 264.5 g. of phenol.

Yield on the phenol-% By distilling the reaction mixture under vacuum, the peroxy compounds, the carboxylic acid, the catalyst and the excess phenol are recovered which are recycled in admixture without separating the various components. Finally 9.9 g. of hydroquinone and 15.5 g. of catechol'are recovered.

EXAMPLE 5 It has been performed in the identical manner. as Example 4 only using 0.018 g. of p.toluensulphonic acid instead of trichloroacetic acid. The same conversion was obtained with a yield on the converted phenol as high as 88%; the catecholzhydroquinone ratiowas also the same.

I claim: I

1. A process for the preparation of catechol and hydroquinone in admixture comprising hydroxylating phenol with hydrogen peroxide in the presence of an alkanoic acid having 1 to 4 carbon atoms and trifiuoroacetic acid present in an amount between 0.2

and 10% by moles with respect to phenol at a temperature between 50 and C. wherein the molar ratio of phenolzhydrogen peroxide is between 20:1 and 4: 1. I

References Cited UNITED STATES PATENTS 3,514,490 5/1970 Marlard 260-6216 HOWARD T. MARS, Primary Examiner N. MORGENSTERN, Assistant Examiner UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,836,591

DATED September 17, 1974 INV ENTOR(S) Paolo MAGGIONI It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract of the Disclosure, line 5,

change "50 100C" to 0 50C Claim 1, line 8, change "50 and 100C" to 0 and 50C Signed and Scaled this Tenth Day of August 1976 [SEAL] Arrest:

RUTH c. msou c. MARSHALL DANN. AIM-fling Office Commissioner of Patent: and Trademarks 

